Unitized electride holder and arm for electric arc furnace electrodes or the like

ABSTRACT

The disclosed structure comprises a combined electrode holder and supporting arm for holding an electric furnace electrode or the like. The holder includes a clamping device mounted on the outer end of a tubular supporting arm which is preferably made of nonmagnetic stainless steel or some other high strength nonmagnetic material. The clamping device includes a contact member or shoe and means for producing clamping pressure between the contact member and the electrode. The electrical current is supplied to the contact member by a bus tube extending longitudinally within the tubular supporting arm, preferably along the axis thereof. The contact member and the bus tube are made of copper or some other material having high electrical conductivity. Within the tubular supporting arm the bus tube is surrounded by a shielding tube made of copper or some other material having high electrical conductivity. Generally, the shielding tube is electrically insulated from the bus tube and the supporting arm, although an electrical connection between one end of the shielding tube and the corresponding end of the supporting arm is permissible. The shielding tube acts as a magnetic shield around the bus tube and thus prevents the supporting arm from being heated by eddy currents induced in the supporting arm by the magnetic field around the bus tube. The shielding tube confines the magnetic field of the bus tube to the space between the bus tube and the shielding tube.

United States Patent Wunsche et al.

[451 Aug. 22, 1972 [21] Appl. No.: 176,138

[52] US. Cl. ..13/15 [51] Int. Cl ..H05b 7/10, F27d 11/10 [58] Field ofSearch ..'.l3/l4,15,16

[56] References Cited I UNITED STATES PATENTS 1,856,330 5/1932 Greene13/16 UX 3,072,732 l/1963 Maloney ..l3/l5 X 3,602,624

Primary Examiner-Roy N. Envall, Jr. Attorney-Burmeister, Palmatier 8LHamby [57] ABSTRACT The disclosed structure comprises a combined elec-8/1971 Turner ..l3/l5 trode holder and supporting arm for holding anelectric furnace electrode or the like. The holder includes a-clampingdevice mounted on the outer end of a tubular supporting arm which ispreferably made of nonmagnetic stainless steel or some other highstrength nonmagnetic material. The clamping device includes a contactmember or shoe and means for producing clamping pressure between thecontact member and the electrode. The electrical current is supplied tothe contact member by a bus tube extending longitudinally within thetubular supporting arm, preferably along the axis thereof. The contactmember and the bus tube are made of copper or some other material havinghigh electrical conductivity. Within the tubular supporting arm the bustube is surrounded by a shielding tube made of copper or some othermaterial having high electrical conductivity. Generally, the shieldingtube is electrically insulated from the bus tube and the supporting arm,although an electrical connection between one end of the shielding tubeand. the corresponding end of the supporting arm is permissible. Theshielding tube acts as a magnetic shield around the bus tube and thusprevents the supporting arm from being heated by eddy currents inducedin the supporting arm by the magnetic field around the bus tube. Theshielding tube confines the magnetic field of the bus tube to the spacebetween the bus tube and the shielding tube.

19 Claims, 5 Drawing Figures UNITIZED ELECTRIDE HOLDER AND ARM FELECTRIC ARC FURNACE ELECTRODES OR THE LIKE This invention relates toelectrode holders for electric arc furnace electrodes or the like. Theelectrode holder is preferably combined or unitized with a supportingarm.

One object is to provide a new and improved electrode holder having acontact member or shoe which is supplied with an electrical current by abus member or tube which extends longitudinally within a tubularsupporting arm. In the absence of the present invention, it has beenfound that a large amount of heat is generated in the tubular supportingarm due to eddy currents induced by the magnetic field around the bustube.

In accordance with the present invention, such heating of the supportingarm is prevented by surrounding the bus tube with a shielding tube madeof a material having a high electrical conductivity. The bus tube iselectrically insulated from the shielding tube, although a connectionbetween one end of the bus tube and one end of the shielding tube wouldbe permissible under appropriate conditions. The shielding tube is alsopreferably insulated from the supporting arm, although a connectionbetween one end of the shielding tube and the corresponding end of thesupporting arm is permissible, if the shielding tube is insulated fromthe bus tube. The shielding tube confines the magnetic field around thebus tube to the space between the bus tube and the shielding tube. Thus,the shielding tube eliminates any mutual inductance or coupling betweenthe bus tube and the supporting arm. The shielding tube also eliminatesmutual inductance or coupling between the bus tubes of adjacentelectrode holders.

In the usual electric furnace, there are several electrodes supported bya corresponding number of electrode holders which are effective toconnect the electrodes to the various phases of a multiphase electricalsystem. The shielding tube minimizes the mutual inductance between thevarious phases. Such mutual inductance can be troublesome in that it cancause unbalanced conditions with regard to the currents supplied to theelectrodes by the various phases. The resulting inequality in theheating produced by the various phases is minimized by the presentinvention.

The supporting arm is preferably made of nonmagnetic stainless steel orsome other high strength nonmagnetic material. The use of a nonmagneticmaterial obviates the heating that can be produced in a magneticmaterial by hysteresis effects due to magnetic fields around theelectrodes.

Further objects, advantages and features of the present invention willappear from the following description, taken with the accompanyingdrawings, in which:

FIG. 1 is a longitudinal section taken through a unitized electrodeholder and arm, to be described as an illustrative embodiment of thepresent invention.

FIG. 2 is an outer end view taken as indicated by the line 22 in FIG. 1.

FIG. 3 is a vertical section taken through the arm, generally along theline 33 in FIG. 1.

FIG. 4 is a horizontal longitudinal section taken through the electrodeholder and arm.

FIG. 5 is a vertical section taken generally along the line 5--S in FIG.4. It will be seen that the drawings illustrate a unitized electrodeholder and arm 10 for holding a cylindrical electrode 12, which may beof the type employed in an electric arc furnace or the like. The unit 10comprises a clamping device 14 mounted on the outer end of a supportingarm 16.

The clamping device 14 is generally annular in shape and extends aroundthe electrode 12. The clamping device includes a contact member or shoe17 for supplying an electrical current to the electrode 12. The contactshoe 17 is made of copper or some other material having high electricalconductivity. It will be seen from FIG. 4 that the contact shoe 17 has acylindrically curved surface 18 for engaging the electrode 12. Coolantpassages 20 are preferably formed in the shoe 17 to provide for thecirculation of cooling water or some other fluid coolant. The coolantpassages 20 may be drilled or otherwise formed. However, it isparticularly advantageous to form the coolant passages in the mannerdisclosed and claimed in the Turner US. Pat. No. 2,997,51 l, issued Aug.22, 1961.

The clamping device 14 includes means for producing clamping pressurebetween the electrode l2 and the contact shoe 17. As shown, the clampingpressure is developed by a movable clamping member or shoe 22 mounted ona clamping band 24 in opposition to the contact shoe 17. However, thecontact shoe 17 could also be movable to develop the clamping pressure.

In this case, the force to actuate the clamping shoe 22 is produced bymeans 26 operable by fluid pressure, such means being illustrated ascomprising a piston 28 movable in a cylinder 30 and sealed by a bellows32. Hydraulic fluid or some other fluid under pressure is supplied tothe cylinder 30 by a pipe 34 connected to a passage 36 which leads intothe cylinder. The illustrated fluid pressure operated device is arrangedto apply the clamping pressure, but the arrangement may also be suchthat the clamping pressure is applied by a spring and is released by thefluid pressure operated device.

The clamping band 24 is made double walled to provide passages 38therein for the circulation of water or some other fluid coolant.Coolant passages 40 may also be provided in the clamping shoe 22. Asindicated in FIGS. 1 and 2, flexible conduits 42 may be employed tocirculate the fluid coolant to and from the clamping shoe 22. Suchflexible conduits are preferably made of metal to withstand the heatinvolved.

The illustrated supporting arm 16 is generally tubular and is preferablymade of nonmagnetic stainless steel or some other highstrengthnonmagnetic material. The use of nonmagnetic material obviateshysteresis losses in the supporting arm. Preferably, the supporting armis double walled to provide passages 44 for the circulation of a fluidcoolant. As shown to best advantage in FIG. 3, the illustratedsupporting arm 16 comprises a rectangular outer wall or tube 46 and acylindrical inner wall or tube 48.

The clamping band 24 is welded or otherwise secured to the outer end ofthe supporting arm 16, as will be evident from FIG. 4. The contact shoe17 is also suitably mounted on the outer end of the supporting arm 16.As shown, a mounting plate or member 50 is mounted on the arm 16 to backup the contact shoe 17.

Means are preferably provided to insulate the contact shoe 17 from thesupporting arm 16 and the clamping band 24. As shown in FIGS. 1 and 4,thin members 52 of electrically insulating material are provided forthis purpose.

Electrical current to energize the contact shoe 17 is supplied to theshoe by a bus tube or member 54, extending within the hollow tubularsupporting arm 16. This location of the bus tube provides a highlycompact construction. It will be seen that the bus tube 54 extendslongitudinally within the supporting arm 16 and has a portion 56 whichprojects beyond the inner end of the supporting arm. A connecting member58 is secured to the projecting portion 56 and is adapted to beconnected to one or more flexible cables leading to a source ofelectrical current. The bus tube 54 and the connecting member 58 aremade of copper or some other material having a high electricalconductivity.

The bus member 54 could be solid, but is preferably tubular to provide apassage 60 therein for the circulation of cooling water or some otherfluid coolant. The passage 60 is preferably employed to carry the fluidcoolant to or from the contact shoe 17. An additional pipe or tube 62 ispreferably provided to complete the circuit for the circulation of thefluid coolant to and from the contact shoe 17. As shown, the coolantpipe 62 is coaxially disposed within the bus tube 54. Preferably, thebus tube 54 is axially disposed within the supporting arm 16.

In accordance with the present invention, a shielding tube 64 isprovided around the bus tube 54 and within the tubular supporting arm16. The shielding tube 64 is made of copper or some other materialhaving a high electrical conductivity. Other examples of such highlyconductive materials are silver and high conductivity aluminum. The bustube 54 and the shielding tube 64 are preferably cylindrical andcoaxial. The high conductivity shielding tube acts as an effectivemagnetic shield around the bus tube 54 so that the magnetic field aroundthe bus tube is confined to the space between the bus tube 54 and theshielding tube 64. Thus, the shielding tube 64 eliminateselectromagnetic induction or coupling between the bus tube 54 and thetubular supporting arm 16. In the absence of the shielding tube 64, suchelectromagnetic induction generates eddy currents of a very considerablemagnitude in the metal walls of the supporting arm 16. These eddycurrents cause heating of the supporting arm so that a great deal ofenergy is wasted. Moreover, the heating may be so great as to bedestructive.

The shielding action of the highly conductive tube 64 is due to thecirculating currents which are induced in the shielding tube by themagnetic field around the bus tube 54. Because of the high conductivityof the shielding tube 64, the heat produced by these circulatingcurrents is small and is easily dissipated by the cooling water or otherfluid coolant.

The shielding tube 64 is preferably insulated from the bus tube 54,although a connection at one end would be permissible. As shown, theshielding tube 64 is electrically insulated from the bus tube 54 at bothends and at intermediate points. At the end of the shielding tube 64adjacent the contact shoe 17, the shielding tube is electricallyinsulated from the contact shoe and the bus tube 54 by a thininsulating-layer or member 66. At the opposite or inner end of thesupporting arm 16. the shielding tube 64 is insulated by an annularsupporting member or insulator 68 made of a heat resistant insulatingmaterial. It will be seen that the shielding tube 64 is fitted into abore 70 in the insulator 68. Another bore 72 is formed in the insulator68 to receive a collar 74 moved around the projecting end portion 56 ofthe bus tube 54. The insulator 68 is bolted or otherwise secured to thesupporting arm 16. I

The shielding tube 64 is also preferably insulated from the tubularsupporting arm 16, although an electrical connection at one end ispermissible. In this case, the projecting end of the shielding tube 64,adjacent the insulator 68, is electrically isolated from the supportingarm 16 by electrical insulating member 76. At the end of the illustratedshielding tube 64 adjacent the contact shoe 17 the shielding tube 64 isconnected to the supporting arm 16 by a collar 78 which acts as a spacerbetween the shielding tube 64 and the inner wall 48 of the tubularsupporting arm 16.

The highly conductive shielding tube 64 substantially eliminates anyelectromagnetic coupling between the bus tube 54 and the supporting arm16 so that the current in the bus tube does not induce currents in thesupporting arm. Thus, the heating that would be caused by such inducedcurrents is eliminated.

Moreover, the shielding tube 64 substantially eliminates anyelectromagnetic induction between the bus tubes of adjacent supportingarms in the usual type of electric furnace, utilizing several supportingarms to hold the various electrodes of a multiphase electrical system.The elimination of electromagnetic coupling between the bus tubes of thevarious phases eliminates the troubles that can be caused by suchcoupling. Thus, such coupling between phases can upset the balance thatshould exist between the phase currents. When this balance is upset, theheat generated by the electrodes of the various phases is renderedunequal. The shielding tube of the present invention eliminates orgreatly reduces such inequalities.

It will be seen that a space 80 is provided between the shielding tube64 and the inner wall 48 of the supporting arm 16. Cooling water or someother fluid coolant is preferably circulated through the space 80.Cooling water can also be circulated through the space 82 between thebus tube 54 and the shielding tube 64, but this is not usually necessaryand may cause losses due to currents induced in the water by the intensemagnetic field in this space.

With the shielding tube of the present invention, there is no heating ofthe supporting arm due to currents induced by the bus tube. Thus, thesupporting arm is protected against damage due to excessive heatmg.

The positioning of the bus tube within the supporting arm provides ahighly compact construction which makes it possible to group theelectrodes of the various phases around a'pitch circle of smallerdiameter. The more compact construction reduces the mechanical stressesin the structure and also reduces the cost of maintenance.

We claim:

1. Electrode holder means for an electric furnace electrode or the like,

comprising an annular clamping device adapted to be mounted around theelectrode,

said clamping device including a contact member for making an electricalcontact with the electrode,

said contact member being made of a material having high electricalconductivity,

said clamping device including means for developing clamping pressurebetween the electrode and said contact member,

a hollow generally tubular supporting arm mechanically connected to saidclamping device to afford support for the electrode and the clampingdevice,

a bus member electrically connected to said contact member and extendinglongitudinally within said hollow generally tubular supporting arm totransmit electrical current to said contact member,

said bus member being made of a material having high electricalconductivity,

a shielding tube extending around said bus member and disposedlongitudinally within said hollow generally tubular supporting arm,

said shielding tube being made of a non-magnetic material having highelectrical conductivity the conductivity of at least comparable to highconductivity aluminum to provide a magnetic shield between said busmember and said supporting arm,

said arm thereby being protected against heating due to eddy currentsinduced by the current in said bus member,

and insulating means providing electrical insulation between at leastone end of said bus member and the corresponding end of said shieldingtube while also providing electrical insulation between at least one endof said shielding tube and the corresponding end of said supporting arm.

2. Electrode holder means according to claim 1,

in which said contact member, said bus member and said shielding tubeare made of copper.

3. Electrode holder means according to claim 1,

in which said bus member is made of copper.

4. Electrode holder means according to claim 1,

in which shielding tube is made of copper.

5. Electrode holder means according to claim 1,

in which said shielding tube is made of aluminum having high electricalconductivity.

6. Electrode holder means according to claim 1,

in which said supporting arm is made of high strength nonmagneticmaterial.

7. Electrode holder means according to claim 1,

in which said supporting arm is made of nonmagnetic stainless steel.

8. Electrode holder means according to claim 1,

in which said insulating means includes an insulator mounted on saidsupporting arm and affording support for one end of said bus member andthe corresponding end of said shielding tube.

9. Electrode holder means according to claim 1,

in which said insulating means includes means affording electricalinsulation between said contact member and said supporting arm.

10. Electrode holder means according to claim 1,

including means for circulating a fluid coolant through said clampingdevice, said contact member, said bus member, and said supporting arm.

1 l. Electrode holder means according to claim 1,

in which said clamping device includes means for exerting clamping forceagainst the electrode in opposition to said contact member.

12. Electrode holder means accordi g to claim 1, in which said clampingdevice "16 udes a clamping member for engaging the electrode inopposition to said contact member,

' and means for developing a clamping force against said clamping memberto produce clamping pressure between said clamping member and saidelectrode and also between said electrode and said contact member.

13. Electrode holder means according to claim 1,

in which said clamping device includes a clamping member movable againstsaid electrode in opposition to said contact member,

and fluid pressure actuated means for developing clamping force againstsaid clamping member to develop clamping pressure between said clampingmember and said electrode and also between said electrode and saidcontact member.

14. Electrode holder means according to claim 1,

in which said bus member extends from said contact member and throughthe entire length of said supporting arm,

said bus member having means projecting beyond the end of saidsupporting arm and including means for connecting the bus member to asource of electrical current,

said shielding tube extending around said bus member within saidsupporting arm.

15. Electrode holder means according to claim 1,

in which said bus member and said shielding tube are coaxial.

l6. Electrode holder means according to claim 1,

in which said bus member and said shielding tube are generallycylindrical and coaxial.

l7. Electrode holder means according to claim 1,

in which said bus member and said shielding tube are coaxial with saidsupporting arm.

18. Electrode holder means according to claim 1,

in which said bus member is in the form of a tube.

19. Electrode holder means according to claim 1,

in which said bus member is in the form of a generally cylindrical tubecoaxial with said shielding tube.

1. Electrode holder means for an electric furnace electrode or the like,comprising an annular clamping device adapted to be mounted around theelectrode, said clamping device including a contact member for making anelectrical contact with the electrode, said contact member being made ofa material having high electrical conductivity, said clamping deviceincluding means for developing clamping pressure between the electrodeand said contact member, a hollow generally tubular supporting armmechanically connected to said clamping device to afford support for theelectrode and the clamping device, a bus member electrically connectedto said contact member and extending longitudinally within said hollowgenerally tubular supporting arm to transmit electrical current to saidcontact member, said bus member bEing made of a material having highelectrical conductivity, a shielding tube extending around said busmember and disposed longitudinally within said hollow generally tubularsupporting arm, said shielding tube being made of a non-magneticmaterial having high electrical conductivity the conductivity of atleast comparable to high conductivity aluminum to provide a magneticshield between said bus member and said supporting arm, said arm therebybeing protected against heating due to eddy currents induced by thecurrent in said bus member, and insulating means providing electricalinsulation between at least one end of said bus member and thecorresponding end of said shielding tube while also providing electricalinsulation between at least one end of said shielding tube and thecorresponding end of said supporting arm.
 2. Electrode holder meansaccording to claim 1, in which said contact member, said bus member andsaid shielding tube are made of copper.
 3. Electrode holder meansaccording to claim 1, in which said bus member is made of copper. 4.Electrode holder means according to claim 1, in which shielding tube ismade of copper.
 5. Electrode holder means according to claim 1, in whichsaid shielding tube is made of aluminum having high electricalconductivity.
 6. Electrode holder means according to claim 1, in whichsaid supporting arm is made of high strength nonmagnetic material. 7.Electrode holder means according to claim 1, in which said supportingarm is made of nonmagnetic stainless steel.
 8. Electrode holder meansaccording to claim 1, in which said insulating means includes aninsulator mounted on said supporting arm and affording support for oneend of said bus member and the corresponding end of said shielding tube.9. Electrode holder means according to claim 1, in which said insulatingmeans includes means affording electrical insulation between saidcontact member and said supporting arm.
 10. Electrode holder meansaccording to claim 1, including means for circulating a fluid coolantthrough said clamping device, said contact member, said bus member, andsaid supporting arm.
 11. Electrode holder means according to claim 1, inwhich said clamping device includes means for exerting clamping forceagainst the electrode in opposition to said contact member. 12.Electrode holder means according to claim 1, in which said clampingdevice includes a clamping member for engaging the electrode inopposition to said contact member, and means for developing a clampingforce against said clamping member to produce clamping pressure betweensaid clamping member and said electrode and also between said electrodeand said contact member.
 13. Electrode holder means according to claim1, in which said clamping device includes a clamping member movableagainst said electrode in opposition to said contact member, and fluidpressure actuated means for developing clamping force against saidclamping member to develop clamping pressure between said clampingmember and said electrode and also between said electrode and saidcontact member.
 14. Electrode holder means according to claim 1, inwhich said bus member extends from said contact member and through theentire length of said supporting arm, said bus member having meansprojecting beyond the end of said supporting arm and including means forconnecting the bus member to a source of electrical current, saidshielding tube extending around said bus member within said supportingarm.
 15. Electrode holder means according to claim 1, in which said busmember and said shielding tube are coaxial.
 16. Electrode holder meansaccording to claim 1, in which said bus member and said shielding tubeare generally cylindrical and coaxial.
 17. Electrode holder meansaccording to claim 1, in which said bus member and said shielding tubeare coaxial with said supporting arm.
 18. Electrode holder meansaccording to claim 1, in which said bus member is in the form of a tube.19. Electrode holder means according to claim 1, in which said busmember is in the form of a generally cylindrical tube coaxial with saidshielding tube.